Alan Turner OBE said he and 10 others watched in amazement as "six or seven" unexplainable blips appeared on radar they were monitoring.

Mr Turner was duty military supervisor at RAF Sopley, in Hampshire, when the inexplicable events unfolded.

He said: "The duty civil supervisor drew my attention to a situation on radar the likes of which neither of us had ever encountered.

"Emanating from a point some twenty nautical miles east of the eastern extremity of the Salisbury Plain danger area were a series of six or seven blips moving on a south-easterly track each being separated from the other by about six miles."

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He said: "I am at a loss to explain what I, and many other people, saw.

"In those days aircraft could not climb at such a rate. To be seen on displays by three different ground radars, plus the airborne radar in the Canberra, is also a mystery."

Details of the case, which happened in the summer of 1971, have been revealed by veteran British UFO investigator Philip Mantle, as one of his most memorable investigations, as he prepares to retire from the UFO conference scene.

Mr Mantle will recount this and a number of other UFO cases at the Outer Limits Magazine UFO conference in Hull on September 9.